As is well known, there are two types of coated fabrics which can be produced by a wet or dry coating process, namely, one in which the resin coat is porous and the other in which the resin coat is non-porous. Generally, when the resin coat is porous, it may provide satisfactory water-vapor transmission but may not provide any sufficient degree of waterproofness. Conversely, when the resin coat is non-porous, it may exhibit good waterproofing performance but may not provide any good permeability to water vapor. For example, coated fabrics produced by a polyurethane resin wet coating process primarily have a high degree of waterproofness, but they have no sufficient permeability to water vapor; as such, it is a common practice to use in combination an anionic surface active agent, a nonionic surface active agent, a hydrophilic polymer, and the like in order to provide improved water-vapor permeability. However, coated fabrics resulting from such practice have no sufficient water vapor transmission and their waterproof performance is considerably lower than what it should be. Apparently, such practice has not been successful in meeting the necessary performance criteria in respect of both moisture permeability and waterproofness.
Recently, in an attempt to overcome such deficiencies, it has been proposed to form on the fibrous base fabric a porous, highly permeable resin coat, then a non-porous resin coat on the porous resin coat, thereby to provide both good water vaper transmission and good waterproofness. With such a method, however, it is only possible to provide a moisture permeability of the order of 5000-6000 g/m.sup.2 /24 hrs at best with respect to the porous, highly permeable resin coat, where a wet process is employed; therefore, even if the non-porous resin coat is applied thinly over the porous resin coat, the permeability of the coated fabric will be extremely low after all. In actuality, therefore, it has been impracticable to meet the requirements for both moisture permeability and waterproofness in a manner consistent with each other. Further, the foregoing approach is disadvantageous from the view point of processing cost in that coating must be effected in two operations.
In Japanese Patent Application Laid-Open Publication No. 58-4873 and Japanese Patent Publication No. 62-53632 are proposed processing methods for production of a water-vapor permeable, waterproof fabric wherein a polyurethane resin film is formed which consists mainly of silicon dioxide and includes porous particles having a mean particle diameter of 2-50 .mu.m and a total pore volume of 0.2-5 ml/g, a water repellent having perfluoro alkyl groups being then applied to the coated fabric. In either of the methods, however, the permeability obtainable is of the order of 3000 g/m.sup.2 /24 hrs at best, which is far from being said to be sufficient.
In Japanese Patent Application Laid-Open Publication No. 2-251672, there is disclosed an invention which concerns a method for production of a polyester coated fabric including a resin coat having fine pores smaller than 150 .ANG. and inorganic porous particles of silicon dioxide, titanium oxide, and the like having a surface area of more than 200 m.sup.2 /g as dispersed densely in layers. However, this particular invention is only intended to prevent the migration of disperse dyes and does not provide sufficient water vapor transmission.